As typical hair dye compositions, mention may be made of a two-part permanent hair dye composition composed of a first part containing an alkaline agent, an oxidation dye and optionally a direct dye such as a nitro dye and a second part containing an oxidizing agent; and a single-part semi-permanent hair dye composition containing an organic acid or an alkaline agent, and at least one type of direct dye such as an acid dye, a basic dye and a nitro dye.
The permanent hair dye has a drawback in that the color tone of hair imparted by an oxidation dye is not so vibrant. Attempts to use a direct dye in combination with an oxidation dye are generally, made to obtain vibrant color. However, a direct dye, in particular, a nitro dye, has a problem in that the color of hair dyed significantly fades. More specifically, the color tone of the hair, even if it is vibrant immediately after dyeing, quickly loses vibrantness (see, for example, Patent Document 1).
A direct dye to be used in combination with an oxidation dye must be stable to a peroxide during a hair-dyeing process. For this reason, the range of direct dyes is limited.
In any one of acid dyes, basic dyes and nitro dyes used in permanent hair dyes and semi-permanent hair dyes, the color of hair quickly fades because the hair loses a direct dye therefrom by washing and exposure to light. This phenomenon is significantly seen in damaged hair.
In such circumstance, as one of the solutions to deal with resistance (fastness) to light, washing, perspiration, friction and heat, it has been proposed to use a direct dye having a dissociative proton in a hair dye (Patent Document 2). The dissociative proton is derived from a phenolic hydroxy group. When a proton is dissociated, anion species are produced, which will contribute to fastness. However, a phenolic hydroxy group dissociates within limited conditions. The limited conditions are also applied to a hair dye composition. Such a limitation can be avoided if a triazene compound having a triazene-1,3-diyl group, which dissociates in different conditions from a phenolic hydroxy group, is used in combination. However, hair dyes containing a triazene compound presently known are not concerned with such dissociation and fail to have excellent fastness (Patent Document 3). In this technical proposal, a hair dye contains a triazene compound not as a direct dye. The proposal only provides a method in which a triazene compound is applied to hair in combination with a water soluble coupling component (a secondary component) and thereafter reacted with the coupling component to produce a compound, which is used as a dye.
[Patent Document 1] JP-A-6-271435
[Patent Document 2] JP-A-2006-182653
[Patent Document 3] JP-A-2006-511721